Your top performing message each month is the message with the highest impression to conversion rate. Impression to conversion rate is calculated by dividing the conversions associated with a message by the impressions that message has had, and then converting it to a percentage by multiplying by 100. This will be significantly lower than the click to conversion rate, as there are more impressions on messages than clicks. This metric is more meaningful as it takes into account the performance of the message across the full funnel, not just the last section of the guest journey.
We only look at messages with more than zero impressions when calculating the top performing message. Out of these we do a second check across your messages and only compare messages with at least half the median impressions for your account over the last month. This ensures we filter out results for messages with less stable results, and celebrate the performance of truly well created messages.
Here is an example of how these rules are applied across a sample set of message data to rank the highest performing message.